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---
title: Graphics Processing Unit (GPU)
type: component
summary: Drawing processor and display controller of the PlayStation.
category: Hardware
---

## Overview

The PlayStation has two graphics processors: the GPU and the GTE (Geometry Transformation Engine).[^hw33]

The GPU and the GTE connect to the CPU as shown in [System Architecture](/hardware/system-architecture/).

The GPU draws polygons and sprites into the frame buffer. It also displays areas of the frame buffer on the screen.[^hw33]

The GTE is a coprocessor of the CPU. It calculates coordinate data and light source data.[^hw33]

## Frame Buffer

The GPU has 1 MB of video memory (VRAM).[^hw33]

The frame buffer is 1024 x 512 pixels.[^hw35]

The frame buffer is dual ported. The GPU can draw into it while the display reads from it.[^hw33]

DMA can transfer data between the frame buffer and main memory.[^hw33]

## Display Area

The GPU displays a rectangular area of the frame buffer on the screen. Sony calls this area the display area.[^hw33]

## Screen Modes

The GPU supports the following screen modes:

Table: Window resolutions

| Mode | Standard resolution (NTSC) | Remarks |
| --- | --- | --- |
| 0 | 256 x 240 | Non-interlace |
| 1 | 320 x 240 | Non-interlace |
| 2 | 512 x 240 | Non-interlace |
| 3 | 640 x 240 | Non-interlace |
| 4 | 256 x 480 | Interlace |
| 5 | 320 x 480 | Interlace |
| 6 | 512 x 480 | Interlace |
| 7 | 640 x 480 | Interlace |
| 8 | 384 x 240 | Non-interlace |
| 9 | 384 x 480 | Interlace |

## Display Colors

The GPU has two display color modes: 15-bit direct and 24-bit direct.[^hw34]

### 15-bit Direct Mode

15-bit direct mode displays up to 32,768 colors.[^hw34]

The GPU computes color in 24 bits and dithers the result. The display comes close to 24-bit color.[^hw34]

### 24-bit Direct Mode

24-bit direct mode displays up to 16,777,216 colors.[^hw34]

The GPU cannot draw in this mode. Drawing assumes 16 bits per pixel.[^hw34]

This mode displays image data that was transferred into the frame buffer.[^hw34]

Frame buffer coordinates stay in 16-bit units. A 640 x 480 image in 24-bit mode occupies 960 x 480 in the frame buffer.[^hw34]

## Drawing Functions

The GPU has the following drawing functions:

Table: GPU drawing capabilities

| Name | Description |
| --- | --- |
| Sprite drawing | 1 x 1 to 256 x 256 pixels. 4-bit CLUT (16 colors per sprite), 8-bit CLUT (256 colors per sprite) or 15-bit direct (32,768 colors per sprite). |
| Polygon drawing | Flat shading. Gouraud shading. Texture mapping. |
| Line drawing | Gradation. |
| Image transfer | CPU to frame buffer. Frame buffer to CPU. Frame buffer to frame buffer. |
| Other | Blending (translucency). Dithering. Clipping. Offset specification. |

## Drawing Coordinates

Drawing coordinates are signed 11-bit values. X and Y range from -1024 to 1023.[^hw35]

The coordinate offset sets the drawing origin anywhere in the frame buffer.[^hw35]

The GPU clips all drawing to the current drawing area.[^hw35]

## Sprite Drawing

The GPU draws sprites of up to 256 x 256 pixels. Width and height can each vary up to that size.[^hw35]

Sprite image data sits in a non-display area of the frame buffer. It must be transferred there before the sprite drawing command runs.[^hw35]

### Texture Pages

A 256 x 256 pixel area of sprite patterns in the frame buffer is a texture page.[^hw36]

The size of a texture page in the frame buffer depends on the texture mode.[^hw36]

The TSB parameter of a drawing command gives the page number. The page number of a texture page at (tx, ty) is tpage = ty/16 + tx/64.[^hw36]

The actual tpage value also holds the CLUT mode (4, 8 or 16 bits) and the semi-transparency rate.[^hw36]

### Sprite Pattern Color Modes

Sprites have three color modes: 4-bit CLUT, 8-bit CLUT and 15-bit direct.[^hw36]

A CLUT (color lookup table) is a table of RGB values. Each pixel of a CLUT sprite is an index into it.[^hw36]

A 4-bit CLUT has 16 entries and an 8-bit CLUT has 256 entries. Each entry has the same structure as a 15-bit pixel.[^hw36]

Each sprite can have its own CLUT.[^hw36]

The CBA parameter of a drawing command gives the left coordinate of the CLUT in the frame buffer.[^hw36]

## Polygon Drawing

The GPU draws triangles and rectangles from the screen coordinates of each vertex.[^hw37]

With Gouraud shading each vertex has its own color. The GPU interpolates the colors across the polygon.[^hw37]

Texture mapping applies a 2-dimensional image to a polygon. Texture patterns sit in non-display areas of the frame buffer and are handled like sprite patterns.[^hw37]

## Texture Cache

The texture cache (T-cache) is a high-speed buffer memory between the GPU and the frame buffer. It speeds up drawing.[^hw37]

Each pixel of a texture is likely to be read more than once.[^hw37]

The GPU reads a texture pixel from the T-cache when it is there. Otherwise it reads the frame buffer.[^hw37]

The T-cache holds its data from polygon to polygon. Polygons drawn in a row are faster when their textures fit in the T-cache.[^hw37]

The T-cache is 2K bytes.[^hw38]

The T-cache size in pixels for each pixel mode:

Table: T-cache size

| Pixel Mode | Size (width x length) |
| --- | --- |
| 4 bits/pixel | 64 x 64 pixels |
| 8 | 64 x 32 |
| 16 | 32 x 32 |

## References

[^hw33]: Sony Computer Entertainment Inc. PlayStation Hardware. August 1998. Page 3-3.
[^hw34]: Sony Computer Entertainment Inc. PlayStation Hardware. August 1998. Page 3-4, Table 3-1.
[^hw35]: Sony Computer Entertainment Inc. PlayStation Hardware. August 1998. Page 3-5, Figure 3-2.
[^hw36]: Sony Computer Entertainment Inc. PlayStation Hardware. August 1998. Page 3-6, Figure 3-4, Figure 3-5.
[^hw37]: Sony Computer Entertainment Inc. PlayStation Hardware. August 1998. Page 3-7.
[^hw38]: Sony Computer Entertainment Inc. PlayStation Hardware. August 1998. Page 3-8, Table 3-2.