early 1985 contained of RAM with an option to expand it to Commodore later increased the system memory to due to objections by the Amiga development team. The names of the custom chips were different; Denise and Paula were called Daphne and Portia respectively. The casing of the preproduction Amiga was almost identical to the production version: the main difference being an embossed Commodore logo in the top left corner. It did not have the developer signatures. The Amiga 1000 has a Motorola 68000 CPU running at 7.15909 MHz on NTSC systems or 7.09379 MHz on PAL systems, precisely double the video color carrier frequency for NTSC or 1.6 times the color carrier frequency for PAL. The system clock timings are derived from the video frequency, which simplifies glue logic and allows the Amiga 1000 to make do with a single crystal. In keeping with its video game heritage, the chipset was designed to synchronize CPU memory access and chipset DMA so the hardware runs in real time without wait-state delays. Though most units were sold with an analog RGB monitor, the A1000 also has a built-in composite video output which allows the computer to be connected directly to some monitors other than their standard RGB monitor. The A1000 also has a "TV MOD" output, into which an RF Modulator can be plugged, allowing connection to older televisions that did not have a composite video input. The original 68000 CPU can be directly replaced with a Motorola 68010, which can execute instructions slightly faster than the 68000 but also introduces a small degree of software incompatibility. Third-party CPU upgrades, which mostly fit in the CPU socket, use faster 68020 or 68030 microprocessors and integrated memory, as well as provide support for a 68881 or 68882 FPU. Such upgrades often have the option to revert to 68000 mode for full compatibility. Some boards have a socket to seat the original 68000, whereas the 68030 cards typically come with an on-board 68000. The original Amiga 1000 is the only model to have 256 KB of Amiga Chip RAM, which can be expanded to 512 KB with the addition of a daughterboard under a cover in the center front of the machine. RAM may also be upgraded via official and third-party upgrades, with a practical upper limit of about 9 MB of "fast RAM" due to the 68000's 24-bit address bus. This memory