It’s the stupid hard drive, stupid

I love my new Apple MacBook Pro, but I’ve been frustrated at how slow it seems, compared to my first-generation Intel-based 20-inch iMac. On the face of it, the MacBook Pro should blow the iMac out of the water. However, when the machines are running with lots of applications, the 15-inch MacBook Pro is a tortoise, the iMac is a hare. Starting apps and switching apps seems instant on the iMac, but lags on the MacBook Pro.

Why should that be? Let’s compare specs:

Processor:
The iMac has a 2.0GHz Intel Core Duo
The MacBook Pro has a 2.33GHz Intel Core 2 Duo

(Note: the current iMac models use the Core 2 Duo processor. Mine is over a year old.)

Memory:
Both machines have 2GB of 667MHz DDR2 RAM, in two 1GB sticks

Ethernet:
Both machines have Gigabit Ethernet linked to a GigE switch

Graphics:
The iMac has an ATI Radeon X1600 with 128MB RAM
The MacBook Pro has an ATI Radeon X1600 with 256MB RAM

To make a long story short, what’s killing me is the hard drive. This dawned on me when I started keeping the Apple System Profiler open on my screen. When the machine slowed down, the amount of virtual memory was huge – 8GB, 9GB, 10GB or more. The access speeds out to the spinning drive was clobbering everything. (As I write this blog entry, the MacBook Pro has 65 processes running with 235 threads, and is using 12.14GB of virtual memory. That’s a lot of disk I/O.)

Hard drive interface:
Both machines use Serial ATA, supporting up to 1.5GB/sec. In fact, they both use the same Intel ICH-7M AHCI chip.

Hard drive:
The iMac has a 3.5-inch 250GB Western Digital Caviar WD2500JS drive (pictured), running at 7200RPM with a 300MB/sec interface, 8MB buffer, and 32-step native command queue. It has an average seek time of 8.9ms.

The MacBook Pro uses a 2.5-inch 200GB Toshiba MK2035GSS drive, running at 4200RPM with a 150MB/sec interface, 8MB buffer, and a 4-step native command queue. It has an average seek time of 12ms.

Yep. There it is. My beautiful notebook is creamed by a slowly rotating hard drive with a slow interface. This swamps the benefit of the faster, more advanced microprocessor. Grrrr.

I’m not mad at Apple: Their online system configurator stated that the 200GB drive was a 4200RPM model. If I’d selected a 160GB drive instead, I would have had 5400RPM. I chose capacity over speed. That may have been a mistake.

In today’s multithreading, multitasking world, disk performance matters! Whether you’re running Windows, Linux, Solaris or Mac OS X, all modern operating systems make extensive use of virtual memory. So, next time you spec your server, your desktop or your laptop, get the fastest freakin’ hard drive available – look at interface, look at rotation speed, look at buffer, look at seek time.

A faster disk is going to make as much difference, in real-world performance, as a faster processor. Probably more.