AGP Inline Memory Module (AIMM) also known as Graphics Performance Accelerator (GPA) is an expansion card

Expansion card

The expansion card in computing is a printed circuit board that can be inserted into an expansion slot of a computer motherboard or backplane to add functionality to a computer system via the expansion bus.One edge of the expansion card holds the contacts that fit exactly into the slot...

 that fits in the AGP

Accelerated Graphics Port

The Accelerated Graphics Port is a high-speed point-to-point channel for attaching a video card to a computer's motherboard, primarily to assist in the acceleration of 3D computer graphics. Since 2004 AGP has been progressively phased out in favor of PCI Express...

 slot of PC motherboards based on some Intel chipsets with onboard graphics. It is intended to be a mid-level cost solution between shared graphics memory and dedicated graphics memory found on more expensive discrete AGP expansion card. AIMM cards are special memory modules that are used as dedicated video memory (display cache) to store Z-buffering

Z-buffering

In computer graphics, z-buffering is the management of image depth coordinates in three-dimensional graphics, usually done in hardware, sometimes in software. It is one solution to the visibility problem, which is the problem of deciding which elements of a rendered scene are visible, and which...

 and they usually have 4MB of 32-bit wide SDRAM

Synchronous dynamic random access memory

Synchronous dynamic random access memory is dynamic random access memory that is synchronized with the system bus. Classic DRAM has an asynchronous interface, which means that it responds as quickly as possible to changes in control inputs...

.