CPU and memory
Let's move on to the "heart" of the device, determining its performance and flexibility. The N900 is powered by the Texas Instruments OMAP3430 ARM Cortex-A8 based processor running at 600 MHz. It's the same CPU as in the Omnia HD, iPhone 3Gs, Palm Pre and the upcoming Sony Ericsson Satio. At the moment, it's one of the most powerful processors used in available mobile phones.
The OMAP3430 consists of ARM Cortex A8 application processor running at 600 MHz, PowerVR SGX530 GPU (graphics acceleration processor) and TMS320C64x DSP/ISP (Digital/Image Signal Processor taking care of telephony, data transmission, image processing, etc) running at 430 MHz.
The ARM Cortex A8 (ARMv7-A architecture) is the main core powering the operating system and applications, running at 600 MHz, and delivering up to 2000 Dhrystone MIPS (on a 1 GHz version) and about 1200 MIPS on the 600 MHz one as in the N900 (to compare, ARMv6 architecture based ARM1136 processor used in e.g. Nokia N97 provides up to 740 MIPS). This core offers as spectacular features as 13-stage superscalar pipeline (the first superscalar CPU in a Nokia phone) with advanced dynamic branch prediction achieving 2.0 DMIPS/MHz, VFP (vector floating-point computation accelerating voice compression, 3D graphics and audio), NEON (64 and 128 bit SIMD instruction set accelerating multimedia and signal processing), Jazelle RCT (Java acceleration and JIT compilation), Thumb-2 (extended 32-bit instruction set, bit-field manipulation, table branches, and conditional execution), integrated L1 and L2 caches and more.
PowerVR SGX530 is a "Series5" GPU (graphics accelerator) from Imagination Technologies, including pixel, vertex, and geometry shader hardware. It includes fully programmable universal scalable shader architecture and delivers performance of 14 MPolys/s and full support for OpenGL ES 2.0. To compare, Nokia's OMAP2420-based phones (e.g. the E90) contain older PowerVR MBX GPU supporting OpenGL ES 1.x, and Freescale MXC300-30 based ones (like the N97, 5800 XpressMusic, N75, etc.) do not contain a GPU at all. N900's GPU is the same as of the iPhone 3Gs (some sources say that the iPhone 3Gs has a slightly more powerful SGX535, but it's not fully confirmed).
The TMS320C64x DSP/ISP core (running at 430 MHz) takes care of all kinds of digital signal processing. It frees the main core from having to spend precious cycles on handling baseband (voice communication and data transmission) and speeds up image processing. To compare, OMAP2420-based phones (E90, etc.) include older C55x (rather than 64x) DSP running at 220 MHz (i.e. almost twice slower) and the Freescale MXC300-30 based models incorporate StarCore SC140e DSP operating at up to 250 MHz.
There's really NOTHING one could complain about when it comes to performance and functionality offered by N900's processor, not only when it comes to the offered "raw speed" but also graphics, video and imaging acceleration.
But good news don't end here and the N900 also impresses with its operating memory size, letting the processor fully utilize its possibilities. It not only has 256 MB of operating memory (SDRAM) but also 768 MB of NAND-based virtual memory (swap), making it 1 Gigabyte in total. Who needs more? (it has been brought to my attention in a discussion on Maemo.com forums that swap is actually located on a partition of the built-in eMMC Flash memory, but this somehow conflicts with tech specs @ Forum Nokia where 768 MB NAND is listed, so at the moment I am not sure which one is true; if it's indeed eMMC then it'll be slightly slower).
The following screenshot shows output of "free" command in N900's X-Terminal, listing total, used and free RAM and swap (virtual memory) after a fresh restart. As the amount of free RAM (52 MB) probably doesn't look too impressive at first sight for a Symbian OS phone user, a word of explanation is needed here. Unlike on Symbian OS, where physical RAM is the only available operating memory, Linux (and so the N900) additionally uses swap, i.e. "virtual memory". In huge simplification, active tasks and processes are kept in RAM while inactive (or infrequently used) data are moved to swap. The N900 not only has additional 768 Megabytes of swap, but it is stored in a dedicated, fast NAND memory (or in eMMC, see the updated comment above). That's why the size of free RAM is not even half as important as on Symbian OS, and when checking how much memory you have left for running additional applications you can safely SUM UP the remaining RAM *and* swap, just like on the screenshot below where total free RAM+swap is well over 800 MB. And in case of the N900 it'll always mean hundreds of megabytes, even after many hours or days of uptime and multiple tasks running. When you launch a lot (and I mean A LOT) of apps the machine may slow down a little bit (due to swap handling being slower than real RAM, and the system having to copy data back and forth between swap and RAM) just like e.g. Windows slows down when its pagefile is heavily used, but that's actually the only negative effect. Don't expect to see any "Out of memory" errors on this machine. I tried really hard to get one, and I ended up having over TWO DOZEN of applications running at once and multiple browser windows open, with some 30-40% performance drop being the only result and the system still letting me start new tasks and open new windows... so I just gave up....
|
