Blast processing

Blast Processing was a marketing term coined by Sega of America to advertise the faster processing performance of the Sega Mega Drive (Sega Genesis in that region).

Sonic the Hedgehog 2 was the posterboy for this campaign, being faster than any other platform game at the time. The ad campaign featured commercials with races between two vehicles, with the SNES strapped to one and the Mega Drive strapped to the other.

Sega originally coined the term to refer to the high-speed bandwidth and fillrate of the Mega Drive VDP's DMA controller, but many later assumed it was referring to the 68000 CPU's higher clock rate.

Origins of term

<mediaplayer>File:Blast Processing Commercial.flv</mediaplayer>

According to Sega staff involved in its development and marketing, it was the high-speed DMA controller, rather than the CPU MHz, that the term was actually referring to. According to Sega of America's former technical director Scot Bayless:

“	the PR guys interviewed me about what made the platform interesting from a technical standpoint and somewhere in there I mentioned the fact that you could just "blast data into the DAC's". Well they loved the word 'blast' and the next thing I knew Blast Processing was born.	„
— Scot Bayless

One of the specific DMA programming techniques he was referring to was the mid-frame palette swap, where the color could be changed every scanline, increasing the colors displayed on screen, a technique that was used in Sonic 2:

“	Marty Franz [Sega technical director] discovered that you could do this nifty trick with the display system by hooking the scan line interrupt and firing off a DMA at just the right time. The result was that you could effectively jam data onto the graphics chip while the scan line was being drawn – which meant you could drive the DAC's with 8 bits per pixel. Assuming you could get the timing just right you could draw 256 color static images. There were all kinds of subtleties to the timing and the trick didn't work reliably on all iterations of the hardware but you could do it and it was cool as heck.	„
— Scot Bayless

Many of these DMA programmable techniques were originally intended by the Mega Drive's original product designer Masami Ishikawa:

“	the sprite size could be changed to fill the whole display. It could also display the background screen behind the scrolling window and could change the color of each line. The number of available colors was limited compared to comparable arcade systems, but it could create shadows that matched each character's shape and was also capable of semi-transparency.	„
— Masami Ishikawa

Technical details

For more technical details on Mega Drive, see Mega Drive: Technical specifications and Mega Drive: Blast Processing

The term was used to refer to the following technical details that gave the Mega Drive a faster performance:

CPU

The fact that the main CPU processor was clocked over two times faster than the one in its rival product, the Super NES. Sega's Motorola 68000 processor was clocked at 7.67 MHz, compared to the 3.58 MHz clock speed of Nintendo's Ricoh 5A22 processor. However, this was slightly misleading. This idea of simply comparing CPU clock rates to determine performance, regardless of other characteristics, is commonly known as the "megahertz myth". While Nintendo's 5A22 did run slower in clock cycles per second, it would put out more instructions per clock cycle, giving it a similar MIPS (million instructions per second) performance to Sega's 68000.

The 68000's faster performance came from other advantages, such as a wider 32-bit internal data bus and 16-bit external data bus (the SNES CPU had a 16-bit internal data bus and 8-bit external data bus), faster external data bus clock rate and bandwidth, more registers, 32-bit instructions, and shared codebase with arcade games (where the 68000 saw widespread use).

Console	Sega Mega Drive	Super Nintendo Entertainment System
Main CPU	Motorola 68000	Ricoh 5A22
Clock rate	7.670453 MHz internal, 5.263157 MHz external	3.579545 MHz internal, 2.684658 MHz external
Data bus width	32-bit internal, 16-bit external	16-bit internal, 8-bit external
Registers	16x 32-bit registers	4x 16-bit registers, 4x 8-bit registers
Arithmetic logic units	32-bit ALU (2x 16-bit ALU), 16-bit ALU	16-bit ALU
Word length	16-bit	16-bit
Internal instruction set	16-bit, 32-bit	8-bit, 16-bit
Internal instructions per second	1.3423 MIPS (16/32-bit instructions)	1.5 MIPS (8/16-bit instructions)
Work RAM	64 KB PSRAM (16-bit, 5.263157 MHz)	128 KB DRAM (8-bit, 2.684658 MHz)
Work RAM bandwidth	10.526314 MB/s, 171 KB per frame (NTSC), 204 KB per frame (PAL)	2.684658 MB/s, 43 KB per frame
Work RAM transfer rate	3.835227 MB/s, 62 KB per frame (NTSC), 74 KB per frame (PAL)	2.68 MB/s, 43 KB per frame

DMA

The fact that the Sega Mega Drive's Yamaha YM7101 VDP graphics chipset had a powerful DMA controller that could handle DMA (direct memory access) operations at much faster speeds than the Super Nintendo. The Mega Drive could write to VRAM during active display and VBlank, and had a faster memory bandwidth than the SNES.

The quicker DMA transfer rates and bandwidth gave the Mega Drive a faster performance over the SNES. This included a higher fillrate, higher gameplay resolution, faster parallax scrolling, fast data blitting, high frame-rate with many moving objects on screen, more tiles and large sprites per frame, and various programmable capabilities, such as mid-frame palette swaps (increasing colors per scanline), direct color mode (increasing colors on screen), scaling and rotation effects, ray casting, a bitmap framebuffer, and 3D polygon graphics; the base Mega Drive hardware (without needing any enhancement chips) could render 3D polygons with a performance comparable to the Super FX enhancement chip (itself significantly outperformed by the Mega Drive's optional Sega Virtua Processor enhancement chip).

Console	Sega Mega Drive	Super Nintendo Entertainment System
DMA controller	Sega 315‑5313 VDP (Yamaha YM7101)	Ricoh 5A22
Clock rate	13.423294 MHz	3.579545 MHz internal, 2.684658 MHz external
Video RAM	64 KB VRAM (Dual-Port), 232 bytes VDP cache (CRAM, VSRAM, sprite cache)	64 KB SRAM, 1056 bytes PPU cache (CGRAM, OAM)
Video RAM bandwidth	13.423294 MB/s, 218 KB per frame (NTSC), 258 KB per frame (PAL)	7.15909 MB/s, 116 KB per frame
DMA transfer rate (inactive display)	3.21845 MB/s VRAM, 6.4369 MB/s VDP cache	2.68 MB/s
DMA transfer rate (active display)	VRAM: 1.425561 MB/s (NTSC), 1.712883 MB/s (PAL) VDP cache: 2.851123 MB/s (NTSC), 3.425767 MB/s (PAL)	335 KB/s
Pixel clock rate	6.711647 MHz (VDP)	5.369317 MHz (PPU)
Read fillrate	6.711648 MPixels/s (104,869 tiles/sec), 427 pixels (53 tiles) per scanline	5.369317 MPixels/s (83,895 tiles/sec), 341 pixels (42 tiles) per scanline
Write fillrate (inactive display)	6.4369 MPixels/s (100,576 tiles/sec), 410 pixels (51 tiles) per scanline	5.36 MPixels/s (83,750 tiles/sec), 340 pixels (42 tiles) per scanline
Write fillrate (active display)	2.851123 MPixels/s (NTSC), 3.425767 MPixels/s (PAL) Pixels per frame: 47,579 pixels (NTSC), 68,079 pixels (PAL)	670,000 pixels/s Pixels per frame: 11,148 pixels
Sprite read fillrate	4.90887 MTexels/s, 320 texels per scanline	4.030947 MTexels/s, 256 texels per scanline
Tiles per frame (active display)	Display: 1800 tiles Transfer: 743 tiles (NTSC), 1063 tiles (PAL)	Display: 1395 tiles Transfer: 174 tiles
Sprite display per frame	80 sprites (8×8 to 32×32)	128 sprites (8×8, 16×16), 65 sprites (32×32), 16 sprites (64×64)
Sprite transfer per frame (active display)	NTSC: 80 sprites (8×8 to 24×24), 46 sprites (32×32) PAL: 80 sprites (8×8 to 24×24), 66 sprites (32×32)	128 sprites (8×8), 43 sprites (16×16), 10 sprites (32×32), 2 sprites (64×64)
Sprite display per scanline	20 sprites (8×8 to 16×16), 13 sprites (24×24), 10 sprites (32×32)	32 sprites (8×8), 16 sprites (16×16), 8 sprites (32×32), 4 sprites (64×64)
Display resolutions	Gameplay: 256×224 to 320×480 (default 320×224) Custom: 128×160 to 320×160, 128×224 to 160×224	Gameplay: 256×224 to 256×239 (default 256×224) Hi-res menu: 512×448 to 512×478 (half-pixels)
Scrolling capabilitie	Parallax scrolling, line scrolling, row/column scrolling, overlapping scrolling row/column layers	Parallax scrolling, line scrolling
Background planes	2 scrolling planes, 1 static window plane, 40–64 overlapping scrolling layers (20–32 layers per plane)	1-2 scrolling planes (128–256 colors), 3 planes (128–160 colors), 4 planes (128 colors)
Background plane resolutions	Tilemap: 256×256 to 768×512 and 1024×256 (2 planes) Bitmap: 128×160 to 320×408 and 512×256	256×256 (1–4 planes), 512×512 (1–2 planes), 1024×1024 (1 plane)
Color palettes	512 colors (default), 1536 colors (Shadow/Highlight), 256–512 colors (direct color)	32,768 colors (default), 256–2048 colors (direct color)
Colors on screen	61–64 colors (default), 75–256 colors (mid-frame swap), 183–1536 colors (Shadow/Highlight), 256–512 colors (direct)	128–256 colors (default), 256–2048 colors (direct color)
Colors per tile	16 colors (2 scrolling tilemap planes), 256–512 colors (direct color)	16 colors (1–2 tilemap planes), 8 colors (3 planes), 4 colors (4 planes), 256 colors (direct color)
3D polygon graphics (base hardware)	Geometry: 10,000 vertices/s, 3000 polys/s Rendering: 1600 polys/s (flat), 150 polys/s (textured)	~100 polys/s (flat)
3D polygon graphics (enhancement chips)	SVP: 9000 polys/s (flat), ~800 polys/s (textured)	SFX: 1000 polys/s (flat), ~100 polys/s (textured) SFX2: 2000 polys/s (flat), ~200 polys/s (textured)

External links

• 1UP's Essential 50 - #28 Sonic The Hedgehog
• gamesTM - Gaming News '92 "Hogging the World Stage"