Sega’s first 16-bit console sold out in Japan within two days. Tony Takoushi, writing in ACE in February 1989, reported about 50,000 machines gone at 21,000 yen each. His verdict on the import was “IT IS THE BUSINESS!” A year later the Mega Drive was in America as the Genesis, at about $200 with Altered Beast in the box, and in autumn 1990 Virgin Mastertronic brought it to Britain at £189.99.
What made it matter was the pairing inside: the 68000 that ran the Amiga and the Atari ST, beside the Z80 from Sega’s own Master System, with a Yamaha FM chip related to the ones in Sega’s arcade boards. What made it famous was the fight with Nintendo that followed, and the slogans Sega wrote for it. Sega’s public hardware history lists the processors, memory, graphics and sound. Those headline specifications need context: sprite limits depend on the display mode, and the processor clock differs between PAL and NTSC.
Fast facts
- Maker: Sega.
- Released: 29 October 1988 (Japan); 1989 as the Genesis (North America); autumn 1990 (UK).
- Launch prices: 21,000 yen; about $200; £189.99.
- CPU: Motorola 68000, 7.67 MHz on NTSC machines and 7.60 MHz on PAL, which the console reports about itself in a register.
- Sound CPU: Zilog Z80, about 3.58 MHz on NTSC machines, with 8K of its own RAM.
- Memory: 64K of main RAM; 64K of video RAM; up to 1 MB (8 Mbit) of cartridge ROM in Sega’s overview.
- Video: Sega’s VDP 315-5313: two scrolling playfields and a sprite plane, 320×224 or 256×224.
- Colours: 64 colour registers from a palette of 512; transparent tile/sprite indices and the backdrop have separate roles.
- Sprites: 80 on screen and 20 per line in the 40-cell mode; 64 and 16 in the 32-cell mode.
- Sound: Yamaha YM2612 FM synthesis plus a Texas Instruments 76489 PSG.
The numbers, as Sega documented them
Sprites depend on the mode, and the real limit is dots. The public Plutiedev sprite guide explains the limits; Sega’s Genesis Software Manual (revised February 1992) gives the same mode distinction. In the 40-cell mode (320 pixels across) the VDP allows 80 sprites, 20 on a line and 320 dots on a line. In the 32-cell mode (256 pixels) it allows 64, 16 and 256. The familiar “80 and 20” belongs to the wide mode only.
At 320 pixels across, ten 32-pixel-wide sprites use the full per-line pixel allowance, even though the sprite-count limit is twenty. Sega’s February 1992 manual also illustrates a last sprite cut short when only part of its width fits in the remaining allowance. Narrower sprites can leave room for more objects on the same line.
Colour entries and transparency do different jobs. Colour RAM stores 64 nine-bit values, with three bits each for red, green and blue. Tiles and sprites choose from four palettes of sixteen entries, treating index zero in each palette as transparent. That leaves fifteen visible tile or sprite colours per palette. It does not make the other four entries unusable: the separately selected backdrop can use any of the 64 entries. Plutiedev’s VDP register reference describes that backdrop selection.
The clock depends on the television standard. Sega’s Genesis Software Manual (revised February 1992), p. 72, identifies a PAL/NTSC bit in the version register at $A10001, separate from the domestic/overseas bit. The documented 68000 clocks are about 7.67 MHz for NTSC and 7.60 MHz for PAL; the overview rounds the processor to 8 MHz.
DMA, and who gets the bus
The VDP can fetch data from main memory using direct memory access (DMA). It takes the bus from the 68000 for that transfer, so the main processor waits. The Z80 can continue running from its own memory, but it must wait if it needs the 68000 address space. Sega describes this distinction in the DMA section of its February 1992 manual. A sound driver that stays within the Z80’s own memory can therefore keep working while the 68000 waits.
Transfer capacity is greater during vertical blanking, when the VDP is not fetching the visible picture. Sega’s overview gives a budget of 7,380 bytes over 36 blanking lines, and its DMA chapter compares blanking-time transfers with a fast 68000 copy loop. That is a budget for the described display configuration, not a guarantee for every mode. Games schedule large graphics updates around the available blanking time.
The sound chip’s arcade parentage
Sega’s public hardware history lists six FM voices plus the PSG’s tones and noise. In the Genesis Sound Software Manual of 21 February 1992, Sega compares the YM2612 with the YM2151 used in its arcade machines and with Yamaha’s synthesizer chips.
Each YM2612 FM channel combines four operators to shape its sound. The chip also has an LFO (low-frequency oscillator), two timers and stereo routing. The PSG supplies simpler square-wave tones and noise alongside it.
Sample playback uses FM channel 6’s output instead of adding a seventh voice. A composer using sampled drums or speech therefore has five FM channels left while PCM playback is enabled.
Marketing louder than the manual
In autumn 1990 Sega of America announced a “national advertising blitz” in its customer magazine, Sega Visions, under the line “Genesis Does What Nintendon’t”, built around games it said Nintendo’s console could not offer. Sonic the Hedgehog followed in 1991, and a Sega Visions reader writing in 1993 listed what had changed since he bought his Genesis in autumn 1990: Sega had “lowered the price of the system by $70, packed in Sonic the Hedgehog, and now are giving away Sonic 2”.
The best-known slogan, “Blast Processing”, is also the hardest to pin down. It appears nowhere in Sega’s Genesis Software Manual or its technical bulletins, and nothing in the developer documentation corresponds to it. In June 1993 Sega Visions told a reader that it was real, and that it “allows the Genesis to display one image while loading another into memory, something the SNES cannot do… without it, Sonic would move about as fast as Mario.” The same month Nintendo Power reported that Sega of America’s consumer service and PR firm “didn’t have a well-defined answer” when asked what it was, and concluded: “In essence, Blast Processing means that Sega’s programmers now know what they’re doing.”
In Britain
The Mega Drive reached Britain through Virgin Mastertronic, which already distributed the Master System. ACE reported in August 1990 that the console would cost £189.99 with Altered Beast, with games at £29.99 to £39.99 and 20 titles at launch. By October Computer and Video Games was writing about “Virgin’s official UK Megadrive” as “out and about”.
It was not an instant success. Edge’s 1996 hardware guide judged that its first British Christmas “wasn’t exactly what you would call successful”, and that sales took off only in 1992, when the Super Nintendo arrived and the rivalry between the two machines filled shop shelves and television screens. By Edge’s count Sega had shipped over a million Mega Drives in the UK by the end of that year. The Mega-CD add-on followed in April 1993 at £270.
Sources
- Sega, Sega Hard Encyclopedia, “Mega Drive”: public specifications for the processors, RAM, video and sound. https://www.sega.jp/history/hard/megadrive/
- Plutiedev, “Sprites” and “VDP register reference”: public explanations of mode-dependent sprite limits and backdrop colour selection. https://plutiedev.com/sprites https://plutiedev.com/vdp-registers
- Sega, Genesis Software Manual (© 1989 Sega of Japan, revised February 1992): Technical Overview dated 28 February 1990 (processors, memory, display, sprites, colour, DMA budget, sound chips); terminology, p. 6 (CRAM, VRAM, the 76489 PSG); DMA, p. 26; sprite display capacity, p. 59; the version register, p. 72; the Genesis Sound Software Manual section (February 1992), overview (the YM2612).
- Sega, Genesis Technical Bulletins (1990): searched with the manual for “Blast Processing”; the term does not appear.
- Tony Takoushi, “Sega’s Sweet Sixteen”, ACE issue 17, February 1989: the Japanese launch, 50,000 sold in two days, 21,000 yen.
- Retro Gamer issue 27 (2006), Mega Drive feature: the Japanese launch on 29 October 1988, the American release in 1989 and the British release about a year later.
- Sega, Sega Hard Encyclopedia, “Mega Drive” (web, secondary): the Japanese release date, 29 October 1988, and price, 21,000 yen. https://www.sega.jp/history/hard/megadrive/
- ANALOG Computing issue 79, December 1989, Summer CES report: the Genesis at about $200, packaged with Altered Beast.
- ACE issue 35, August 1990, and issue 37, October 1990, news: the UK price, launch games and Virgin Mastertronic as distributor.
- Computer and Video Games issue 107, October 1990, news: Virgin’s official UK Mega Drive on sale.
- Sega Visions vol. 1 no. 2, October 1990: the “Genesis Does What Nintendon’t” campaign.
- Game Informer issue 2, November 1991: Sonic the Hedgehog on sale.
- Sega Visions, June 1993, letters page: the price cut and Sonic pack-in, and Sega’s explanation of Blast Processing.
- Nintendo Power issue 49, June 1993: “Does the Super NES have Blast Processing?”
- Edge Essential Hardware Guide (special edition, 1996), Mega Drive entry: the UK launch with Altered Beast, the first Christmas, over a million UK sales by the end of 1992, and the Mega-CD in April 1993 at £270.