Motorola 68040
Encyclopedia
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
from Motorola
Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
, released in 1990. It is the successor to the 68030
Motorola 68030
The Motorola 68030 is a 32-bit microprocessor in Motorola's 68000 family. It was released in 1987. The 68030 was the successor to the Motorola 68020, and was followed by the Motorola 68040. In keeping with general Motorola naming, this CPU is often referred to as the 030 .The 68030 features on-chip...
and is followed by the 68060
Motorola 68060
The Motorola 68060 is a 32-bit microprocessor from Motorola released in 1994. It is the successor to the Motorola 68040 and is the highest performing member of the 680x0 family. Two derivatives were produced, the 68LC060 and the 68EC060....
. There was no 68050. In keeping with general Motorola naming, the 68040 is often referred to as simply the '040 .
In Apple Macintosh
Macintosh
The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...
computers, the 68040 was found mainly in the Macintosh Quadra
Macintosh Quadra
The Macintosh Quadra series was Apple Computer's product family of professional high-end Apple Macintosh personal computers built using the Motorola 68040 CPU. The first two models in the Quadra line were introduced in 1991, and the name was used until the Power Mac was introduced in 1994...
, which was named for the chip. The fastest 68040 processor was clocked at 40 MHz and it was only used in the Quadra 840AV. The more expensive models in the (short-lived) Macintosh Centris
Macintosh Centris
Macintosh Centris is a line of Macintosh computers, introduced in 1993, that were built around the Motorola 68LC040 and 68040 CPUs. The name was chosen to indicate that the consumer was selecting a Macintosh in the center of Apple's product line: lower performance than the Quadra computers, but...
line also used the 68040, while the cheaper Quadra, Centris and Macintosh Performa
Macintosh Performa
The Macintosh Performa series was Apple Computer's consumer product family of Apple Macintosh personal computers sold through department stores and mass-market retailers from 1992 until 1997, when it was superseded by the Power Macintosh 5x00 series...
used the 68LC040. The 68040 was also used in other personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
s, such as the Amiga 4000
Amiga 4000
The Commodore Amiga 4000, or A4000, is the successor of the A2000 and A3000 computers. There are two models, the A4000/040 released in October 1992 with a Motorola 68040 CPU, and the A4000/030 released in April 1993 with a Motorola 68EC030....
and Amiga 4000T
Amiga 4000T
The Amiga 4000T, also known as A4000T, was a tower version of the A4000 computer. Using the AGA chipset, it was originally released in small quantities in 1994 with a 25 MHz Motorola 68040 CPU, and re-released in greater numbers by Escom in 1995, after Commodore's demise, along with a new...
, as well as a number of Workstation
Workstation
A workstation is a high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating systems...
s and later versions of the NeXT
NeXT
Next, Inc. was an American computer company headquartered in Redwood City, California, that developed and manufactured a series of computer workstations intended for the higher education and business markets...
computers.
The 68040 was the first 680x0 family member with an on-chip Floating-Point Unit (FPU). It thus included all of the functionality that previously required external chips, namely the FPU and Memory Management Unit
Memory management unit
A memory management unit , sometimes called paged memory management unit , is a computer hardware component responsible for handling accesses to memory requested by the CPU...
(MMU), which was added in the 68030. It also had split instruction and data caches of 4 kilobyte
Kilobyte
The kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
s each. It was fully pipelined
Instruction pipeline
An instruction pipeline is a technique used in the design of computers and other digital electronic devices to increase their instruction throughput ....
, with six stages.
Unfortunately, the 68040 ran into the transistor budget limit early in design. While the MMU did not take many transistors — indeed, having it on the same die as the CPU actually saved on transistors — the FPU certainly did. Motorola's 68882
Motorola 68881
The Motorola 68881 and Motorola 68882 were floating-point coprocessor chips that were used in some computer systems in conjunction with the 68020 or 68030 CPUs. The addition of one of these chips added substantial cost to the computer, but added a floating point unit that could rapidly perform...
external FPU was known as a very high performance unit and Motorola did not wish to risk integrators using the "LC" version with a 68882 instead of the more profitable full "RC" unit. (For information on Motorola's multiprocessing model with the 680x0 series, see Motorola 68020
Motorola 68020
The Motorola 68020 is a 32-bit microprocessor from Motorola, released in 1984. It is the successor to the Motorola 68010 and is succeeded by the Motorola 68030...
.) The FPU in the 68040 was thus made incapable of IEEE transcendental function
Transcendental function
A transcendental function is a function that does not satisfy a polynomial equation whose coefficients are themselves polynomials, in contrast to an algebraic function, which does satisfy such an equation...
s, which had been supported by both the 68881 and 68882 and were used by the popular fractal generating software of the time and little else. The Motorola floating point support package (FPSP) emulated these instructions in software under interrupt. As this was an exception handler, heavy use of the transcendental functions caused severe performance penalties.
Heat was always a problem throughout the 68040's life. While it delivered over four times the per-clock performance of the old-when-released 68020 and 68030, the chip's complexity and power requirements came from a large die and large caches. This affected the scaling of the processor and it was never able to run with a clock rate exceeding 40 MHz. A 50 MHz variant was planned, but canceled. Overclocking
Overclocking
Overclocking is the process of operating a computer component at a higher clock rate than it was designed for or was specified by the manufacturer, but some manufacturers purposely underclock their components to improve battery life. Many people just overclock or 'rightclock' their hardware to...
enthusiasts reported success reaching 50 MHz using a 100 MHz oscillator instead of an 80 MHz part and the then novel technique of adding oversized heat sinks with fans.
The 68040 offered the same features as the Intel 80486
Intel 80486
The Intel 80486 microprocessor was a higher performance follow up on the Intel 80386. Introduced in 1989, it was the first tightly pipelined x86 design as well as the first x86 chip to use more than a million transistors, due to a large on-chip cache and an integrated floating point unit...
, but on a clock-for-clock basis could significantly outperform the Intel chip. However, the 80486 had the ability to be clocked significantly faster without suffering from overheating problems. In late 1991, as the higher-end Macintosh desktop lineup transitioned to the '040, Apple was unable to offer the newer processor in their top-of-the-line PowerBook
PowerBook
The PowerBook was a line of Macintosh laptop computers that was designed, manufactured and sold by Apple Computer, Inc. from 1991 to 2006. During its lifetime, the PowerBook went through several major revisions and redesigns, often being the first to incorporate features that would later become...
s until early 1994. With PowerBooks being restricted to 68030s for several years, Macworld
Macworld
Macworld is a web site and monthly computer magazine dedicated to Apple Macintosh products. It is published by Mac Publishing, which is headquartered in San Francisco, California...
reviewers conceded that the best choice for power users was the PC compatible Texas Instruments
Texas Instruments
Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
80486 notebook, rather than the top-of-the-line PowerBook 180.
Versions of the 68040 were created for specific market segments, including the 68LC040, which removed the FPU, and the 68EC040, which removed both the FPU and MMU. Motorola had intended the EC variant for embedded use, but embedded processors during the 68040's time did not need the power of the 68040, so EC variants of the 68020 and 68030 continued to be common in designs.
Motorola produced several speed grades. The 16 MHz and 20 MHz parts were never qualified (XC designation) and used as prototyping samples. 25 MHz and 33 MHz grades featured across the whole line, but until around 2000 the 40 MHz grade was only for the "full" 68040. A planned 50 MHz grade was canceled after it exceeded the thermal design envelope
Thermal Design Power
The thermal design power , sometimes called thermal design point, refers to the maximum amount of power the cooling system in a computer is required to dissipate. For example, a laptop's CPU cooling system may be designed for a 20 watt TDP, which means that it can dissipate up to 20 watts of heat...
.
For more information on the instructions and architecture, see Motorola 68000
Motorola 68000
The Motorola 68000 is a 16/32-bit CISC microprocessor core designed and marketed by Freescale Semiconductor...
.
68EC040
The 68EC040 is a version of the Motorola 68040 microprocessor, intended for embedded controllers (EC). It differs from the 68040 in that it has neither an FPU nor an MMU. This makes it less expensive and it draws less power.68LC040
The 68LC040 is a low cost version of the Motorola 68040 microprocessorMicroprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
with no FPU. This makes it less expensive and it draws less power. Although the CPU now fits into a feature chart more like the Motorola 68020, it continues to include the 68040's cache
Cache
In computer engineering, a cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere...
s and pipeline and is thus significantly faster than the 68020.
Some mask
Mask (computing)
In computer science, a mask is data that is used for bitwise operations.Using a mask, multiple bits in a byte, nibble, word can be set either on, off or inverted from on to off in a single bitwise operation.-Masking bits to 1:...
revisions of the 68LC040 contained a bug
Software bug
A software bug is the common term used to describe an error, flaw, mistake, failure, or fault in a computer program or system that produces an incorrect or unexpected result, or causes it to behave in unintended ways. Most bugs arise from mistakes and errors made by people in either a program's...
that prevents the chip from operating correctly when a software FPU emulator
Emulator
In computing, an emulator is hardware or software or both that duplicates the functions of a first computer system in a different second computer system, so that the behavior of the second system closely resembles the behavior of the first system...
is used. According to Motorola's errata,http://www.freescale.com/files/microcontrollers/doc/errata/MC68040DE_D.txt any chip with a mask set 2E71M or later does not contain the bug. This new mask was introduced in mid-1995 and converted the 68LC040 chip to MC status.http://www.freescale.com/files/shared/doc/pcn/PCNR00274.html
The buggy revisions are typically found in 68LC040-based Apple Macintosh computers. Chips with mask set 2E23G (as used in the LC 475) have been confirmed to be faulty. The fault relates to pending writes being lost when the F-line exception is triggered.http://gnats.netbsd.org/13078 The 68040 cannot update its microcode in the manner of modern x86 chips. This means that the only way to use software that requires floating-point functionality is to replace the buggy 68LC040 with a later revision, or a full 68040.