8 GB of GDDR5 memory
256 bit bus
~5.5 Ghz data rate
Peak bandwidth - ~176 GB/s.
8 GB of DDR3 memory
256 bit bus
~2.1 Ghz data rate
Peak bandwidth - ~68.3 GB/s
Additionally, the Xbox One has approximately 32 megabytes of embedded SRAM (eSRAM) on the die. Reports suggest that there's approximately 50 GB/s of bandwidth in both directions for the embedded SRAM. We're still not quite sure how the eSRAM is being used - if it's being used as a cache, for example, the Xbox One could come close to matching the PS4's total memory bandwidth. Here's an article from AnandTech that provides a bit more detail.
Memory demands from the OS
Reportedly, the PS4 OS requires about 1 GB of memory, leaving 7 GB for developers. The Xbox One employs 3 different software elements - the Xbox OS, the Windows 8 kernel (thanks amxn), with both being tied together and managed by a hypervisor. The Windows 8 partition reportedly boots when the system is powered on and runs indefinitely until the system powers down. The Xbox OS partition, on the other hand, is booted only when you're playing a game. The hypervisor manages both of these seamlessly, allowing you to multitask between gaming and other entertainment features. It's being speculated that all three software elements consume 3 GB of memory, leaving 5 GB available for developers.
Differences in the types of memory
GDDR5 and DDR3 transmit data in different ways. GDDR5 has a relatively higher latency, but delivers data in larger chunks - exactly what you would want for a GPU, but not necessarily ideal for a CPU. On the other hand, DDR3, the memory type employed by the Xbox One, transmits smaller amounts of data more quickly - this is ideal for a CPU, but not exactly the best option for a GPU.
Here's a thread from r/buildapc from about 4 months ago that goes into a bit more detail regarding the differences.
The architectures of these systems are quite profound, as they reveal the overarching philosophies of both companies. Sony's approach with the GDDR5 is ideal for gaming, as it augments the GPU and is great for developers. Microsoft's choice for DDR3 (and the eSRAM) favors the CPU a bit more and, as a result, is better for activities like multitasking.
Aside from the memory subsystems, it should be noted that the PS4 simply does have more power under the hood, with 50% more raw shader power - 768 SPs at 800mhz for the Xbox One, versus 1152 SPs at 800 mhz for the PS4. Unlike the Playstation 3, this isn't a complicated architecture to understand, and it may not take anywhere near 3+ years for developers to harness this power.
Both systems, however, are exponentially significantly more powerful than the 360/PS3. One of the key features of both next gen systems is that they have unified memory pools. In your current computer, you have system memory, but your graphics card (if it's dedicated) has its own pool of memory as well. As a result, your system has to copy data from one pool of memory to the other, which takes time and can hinder peformance.
The 8 GB memory pools in the PS4/One are unified - meaning, quite simply, that both the CPU and GPU inside the PS4/One access the same pool of memory. This can provide significant performance increases (ie, the CPU can load textures into the memory, while the GPU is rendering). If you're interested in learning more about this, simply perform a search for "hUMA" (heterogeneous unified memory access).
And, even if you only game on a PC, and not a console, you should still be pretty excited, as the new consoles will only raise the bar for PC games. Porting games among the PC, PS4, and Xbox One is going to be far easier. In fact, the developer of Warframe recently said in an interview that Sony asked only 3 months ago if they wanted to bring the game to the PS4. They agreed, Sony sent devkits, and 3 months later, they showed off Warframe footage running on PS4 devkits at E3. Edit - Here's a link to the interview
This is definitely an exciting time to be a gamer.
There seems to be much discussion comparing the next gen consoles against gaming PCs, and I think it's a bit unfair to make such direct comparisons. Many look at the Xbox One and PS4 and come to the conclusion that the consoles have about the same computational power as a Radeon 7850 (for those unaware, this is a mid range graphics card). And, in fact, this may be true. However, developing software for consoles is different than developing software for a PCs. When developing games for PCs, there tends to be a lot of abstraction.
A developer who is making a game to run on a PC has to make a game that can run on a seemingly endless amounts of hardware setups. Developers making a game for a console, on the other hand, know exactly what they're working with, and can extract every single iota of power from the console itself. To analogize this (bear with me) in a somewhat odd way, pretend you're a chef. Your friend comes to you and tells you that there's a wedding taking place, and you need to make all the food for the reception. Well, OK, you could certainly do that successfully, but you may not get the best results. This would be similar to writing a game to run on PCs. Now, let's say your friend comes to you, says you need to make food for the reception, but tells you that there will be exactly 37 guests, 20 male, 17 female, half the males prefer chicken, the other half prefers steak, 1/3 of the females don't drink wine, none of the guests like seafood, and so forth (you get the idea). You know exactly what to make and how much to make to get the absolute best results.
It's not a perfect analogy, but hopefully it gives you an idea of why you can't exactly make a direct comparison between the next gen consoles and a PC of commensurate power. Since developers know exactly what they're working with, they can optimize their engines and games to get the most out of the console version."
~ c_will (reddit)
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